The radiate pseudanthium, with actinomorphic disk flowers surrounded by showy marginal zygomorphic ray flowers, is the most common inflorescence in the Helianthus genus. In Helianthus radula, ray flower primordia are normally absent at the dorsal domain of the inner phyllaries (discoid heads) while the occurrence of radiate inflorescences is uncommon. In Helianthus spp., flower symmetry and inflorescence architecture are mainly controlled by CYCLOIDEA (CYC)‐like genes but the putative role of these genes in the development of discoid inflorescences has not been investigate. Three CYC genes of H. radula with a role in ray flower identity (HrCYC2c, HrCYC2d, and HrCYC2e) were isolated. The phylogenetic analysis placed these genes within the CYC2 subclade. We identified two different alleles for the HrCYC2c gene. A mutant allele, designed HrCYC2c‐m, shows a thymine to adenine transversion, which generates a TGA stop codon after a translation of 14 amino acids. We established homozygous dominant (HrCYC2c/HrCYC2c) and recessive (HrCYC2c‐m/HrCYC2c‐m) plants for this nonsense mutation. Inflorescences of both HrCYC2c/HrCYC2c and HrCYC2c/HrCYC2c‐m plants initiated ray flowers, despite at low frequency. By contrast, plants homozygous for the mutant allele (HrCYC2c‐m/HrCYC2c‐m) failed at all to develop ray flowers. The results support, for the first time, a role of the HrCYC2c gene on the initiation of ray flower primordia. However, also in the two dominant phenotypes, discoid heads are the prevalent architecture suggesting that this gene is required but not sufficient to initiate ray flowers in pseudanthia. Other unknown major genes are most likely required in the shift from discoid to radiate inflorescence.

中文翻译：

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向日葵花序中的射线花起始受 HrCYC2c 基因功能等位基因的影响

放射状的假花是向日葵属中最常见的花序，具有辐射对称的圆盘花，周围环绕着艳丽的边缘左右对称射线花。在向日葵中，内叶脉（盘状头）的背侧区域通常不存在射线花原基，而放射状花序的出现并不常见。在向日葵属中，花对称性和花序结构主要受CYCLOIDEA ( CYC ) 样基因控制，但尚未研究这些基因在盘状花序发育中的假定作用。H 的三个CYC基因。拉杜拉分离出在射线花特性（HrCYC2c、HrCYC2d和HrCYC2e）中起作用的基因。系统发育分析将这些基因置于 CYC2 亚分支内。我们为HrCYC2c基因鉴定了两个不同的等位基因。一个设计为HrCYC2c-m 的突变等位基因显示胸腺嘧啶到腺嘌呤的颠换，在翻译 14 个氨基酸后产生 TGA 终止密码子。我们为这种无义突变建立了纯合显性（HrCYC2c / HrCYC2c）和隐性（HrCYC2c-m / HrCYC2c-m）植物。两者的花序HrCYC2c / HrCYC2c和HrCYC2c/ HrCYC2c-m植物虽然频率较低，但仍会发出射线花。相比之下，突变等位基因（HrCYC2c-m / HrCYC2c-m）纯合的植物根本无法发育出射线花。结果首次支持了HrCYC2c基因在射线花原基起始中的作用。然而，在两种显性表型中，盘状头是普遍的结构，表明该基因是必需的，但不足以在假单胞菌中启动射线花。从盘状花序到辐射状花序的转变很可能需要其他未知的主要基因。